Josephine McDermott - "The first Vertebrate: Discovering how life came to land".

Josephine McDermott - producer & presenter of the BBC's Witness History programme joins David to discuss her programme called "The first Vertebrate: Discovering how life came to land". The programme focuses on Swiss student Iwan Stossel's discovery on Valentia in 1992 of the longest set of footprints made by the first four legged animals ever to walk on earth - 365 million years ago.